CONTROL DEL ARCO ELECTRICO.pdf

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Study about the Process Control of an Electric Arc Furnace using

Simulations based on an Adaptive Algorithm

MANUELA PANOIU1, CAIUS PANOIU1, IOAN ŞORA2, ANCA IORDAN1

1

Faculty of Engineering Hunedoara,2Faculty of Electrical Engineering

Polytechnic University of Timisoara1Revolutiei street nr. 5, cod 331128

2Vasile Parvan street, no. 2, Timisoara, cod 300223

ROMANIA

{c.panoiu, m.panoiu, anca.iordan}@fih.upt.ro, [email protected]

Abstract: - The electric arc furnaces are a very large power load, determining the negative effects on the power

quality (harmonics currents, unbalanced load, and reactive power). For a maximum efficiency of the power

consumption it is necessary to use an automat system for control the harmonics filters, the reactive power

compensation installation and the electrodes position, in order to obtain a high value of power factor and a

maximum efficiency. In this paper is used an adaptive algorithm for process control for an Electric Arc

Furnace. The method is validating using simulation in PSCAD EMTDC software dedicated to Power Systems.

Key-Words: - Adaptive control, LMS algorithm, active power control

1 IntroductionIn the last decade the EAF (Electric Arc

Furnaces) are very large used to the steel making

industry. But, the electrical installation of the

electric arc furnace is a massive generator of thereactive power, harmonics currents and unbalanced

currents. These effects are very harmful for the

electric power supplying line and for the others

consumers. Because the inductive load character of

the electric arc furnace, the reactive power

component are significant, following to the

diminution of the active power factor and therefore

to the decreasing of the efficiency of the electric arc

furnace. In scope of improving the efficiency of the

entire installation it is necessary to use a complex

installation for reactive power compensation,

harmonics current filters and load balancing. Theseinstallations must be connected to an automat

system for an efficient real–time control.

2 Designing the control system of the

EAFThe design of the control system was made

following the measurements made in an industrial

plant. The measurements were made at a 3-phase

power supply installation of a 3-phase EAF of 100 t,

to which were not connected the filters for thecurrent harmonics, neither the load symmetrisation

devices nor reactive power compensation. The

detailed results of these measurements were

presented in [7]. From the ones previously presented

resulted that the elements that contribute to the

development of an action concerning theimprovement of the electric power’s quality can be

grouped in:

- the capacitors fix battery in Y connection used

for compensation of the constant reactive power;

- 14 capacitors battery independently

connectable, in Y connection , used for

compensation of the variable reactive power;

- an Adaptable Balancing Compensator (ABC)

achieved with 3 susceptances controlled by

thyristors in Δ connection used for load

balancing as well as for the compensation of the

difference between the reactive power installedin the capacitors’ batteries and harmonic filters

and the necessary of reactive power until the

obtaining of a unitary power factor;

- 4 filtration blocks of filter in Y connection used

for filtration of current harmonics 5,7,11 and 13.

Using of these installations aiming the

fulfillment of the functions for which they were

designed need the utilization of an intelligent system

of their control. The control system must allow the

on–line determination of the electric values of the

EAF’s installation. The system must also calculate

the necessary step for compensating the reactive power as well as the value of the susceptances

WSEAS TRANSACTIONS on

INFORMATION SCIENCE and APPLICATIONS Manuela Panoiu, Caius Panoiu, Ioan Sora, Anca Iordan

ISSN: 1790-0832 1628 Issue 11, Volume 5, November 2008

mailto:anca.iordan%[email protected]:anca.iordan%[email protected]


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necessary for load balancing. Based on these values,

having in view the chosen constructive solution of

adjustable susceptance with tyristors, is calculated

the control angle of each tyristor;

The diagram of the control system proposed to

be used at the load’s compensation – balancing –

filtration is depicted in fig. 1. In [7], [8] and [5] was

calculated the values of these elements.

Fig. 1.The system diagram for process control of the EAF

3 Simulation of the EAF functioningFor validating the proposed control system it was

made a simulation of the EAF using PSCAD

EMTDC simulation program [10]. For simulation it

was use an electric arc model, depending on the

nonlinearity of the electric arc. This model was

presented in [7] and [8]. Based on this model it was

made a simulation for the entire electrical

installation of the EAF and for the propose control

system. The PSCAD simulation scheme is depicted

in fig. 2.

3.1 The EAF functioning simulation on

controlling the electrodes positionThe electrical items variation in different

functioning regimes can be done only if we consider

an arc length variation between 0, corresponding to

the short-circuit regime, and a maximum value. The

maximum value is determined in such a way that the

electric arc is burning. For observing the variation

area of the powers on the supplying line the active

power meters and reactive power meters was

connecting like in figure 2. The outputs of these

meters permit to obtain the rms values.

The electrodes position controlling is performed

taking into account on the real condition existing on

the considered industrial plant. The maximum

motion speed of the electrodes is of 3 m/min (0.05

m/s) and is reached in emergency regime, its

variation being achieved as in fig. 2; The electric

arc’s length can be modified from zero to a

maximum value determined by limiting the

integrator’s output, fig. 2; The calculus of the dropvoltage is made based on the electric arc model ([7],

[8]), the implementation diagram being also in fig.

2; The electric arc’s length can be modified from

zero to a maximum value. Adjustment of the

electrodes’ position is made independently on each

phase. Simulation of the electric installation’s

operation modifying the electric arc’s length was

made initially without harmonics filters, power

compensation or load balancing. It was considering

the electric arc’s initial value as well as

the electrodes’ initial speed

cm160 =l

321 0=== vvv m/min.Then, was command the lowering-down of the

Impulse Generator Block

for Thiristros Command

(IGBTC)

Ssc=1100 MVA (min.)

FA5 FA7 FA11 FA1314 steps

ADAPTING BLOCK

(AB)

Data acquisition

board

Contactors Block

Command (CBC)

160 MVA3 x TT

30 KV3 x TC

ABC

Furnace

transformer

6 analog

signals





3/10

electrodes up to the fulfillment of the short-circuit

condition. After approximate 8 seconds it was

command, independently on each phase, the lifting-

up of the electrodes with different speeds up to the

considered maximum length of the electric arc

cm26max =l .

Um1

Um2

Im1

Im2

v1

Im3

Um3

Q

P ow er

A B

P Q

A

B

C

A

B

C

.000001 [ohm]

.000001 [ohm]

.000001 [ohm]

P

v2 v3

RMS

Uth1 Uth2 Uth3

A

B Compar-ator 0.0

D+

F

+

-0.5

*

2.0

*

Uth1

A

D+

F

+*

B

l1

Measure acpower

tive

l1

l0

D+

F

+*

v1

l1 l2 l3

TIME

1sT

The threephase electricarc model

A

B

C

A

B

C0.565 [kV]

#2#1

30kV

73.0 [MVA]6.9 e-3 [ohm]9.5422 E-6 [H]

3.64 e-3 [ohm]

0.372e-3[ohm]

8.9416 e-6 [H]

9.5422 e-6 [H]

Ul2

Ul1

RA 1 +

RA 2 +

RA 3 +

IA1

IA2

IA3

Ul3

RMS

RL

RL

A

B

C

RL

A

B

C

A

B

C30 [kV]

#2#1

110 [kV]

100 [MVA]

Electrodes speed control

0.05

-0.05

v1 (m/s)

-0.001

0.05

-0.05

v2 (m/s)

-0.001

0.05

-0.05

v3 (m/s)

-0.011

The HV-MV

transformer

T

(Fu

he MV-LV transformer

rnace transformer)

Measurereactive power

Arc length onphase 1

Arc speed onphase 1

The drop (threshold)voltage on phase 1

Fig. 2. The PSCAD simulation scheme for measure active power and reactive power.

The calculus of the arc length based on the electrodes speed

In this way it was covered practically the entire

operation domain, from the short-circuit regime up

to the fulfillment of the conditions in which the

electric arc does not ignite anymore. The simulationresults are presented in fig. 3 and 4. One can

observe that the highest value of the active power is

obtained when the value of the arc length is

aprox.16 cm. The reactive power is positive

regardless the working regime, having values

between 15-100 MVAR, being therefore necessary

the utilization of the reactive power’s compensation

installation. One can observe that the domain in

which the reactive power should be compensate is

higher than the one chosen in case of designing the

reactive power’s compensation installation from [8].

This is due to the fact that the simulation includedalso the short-circuit regime where the reactive

power, considering the symmetrical short network,

has, according to the circle’s diagram, the value

MVARS Q cnsc 23,1032 =⋅=

(1)In the electrodes’ short-circuit regime are obtained

maximum values of the currents on the three phases,

on the both supply lines and minimum values of the

voltages, fact due to the high loading of the 3-phase

transformers. The rms values of the currents and

voltages, fig. 3, are different between the phases

because the different values of the load impedance

and because of the different values of the arc lengths

on each phase. The different values of the load

impedances are obtained from the values of the

resistances and inductivities from relation (2) and

(3). These are the real values from the electrical





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installation of an EAF in an industrial plant in

Romania.

,0372,0

,3640,0

,6908,0

3

2

1

Ω=

Ω=

Ω=

m R

m R

m R

r

r

r

(2)

.9416,8

,5422,9

2

31

H L

H L L

r

r r

μ

μ

=

== (3)

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0

0

20

40

60

80

100

120

140

160

180

A r c c u r r e n t ( k A )

IA1 IA2 IA3

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

V o l t a g e i n s e c . f u r n a c e t r a n s f

Uj1 Uj2 Uj3

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

C u r r e n t i n p r i m a r y f u r n a c e t r a n s f .

Im1 Im2 Im3

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

V o l t a g e i n p r i m a r y f u r n a c e t r a n s f .

Um1 Um2 Um3

Fig. 3 The rms values for currents and voltages in the secondary in primary voltage transformer





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0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0

0

25

50

A c t i v e p o w e r ( M W )

P

0

25

50

75

100

125

150

R e a c t i v e

p o w e r ( M V A R )

Q

0.0000.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

A r c d r o p v o l t a g e ( k V )

Ust1 Ust2 Ust3

0.000

0.050

0.100

0.150

0.200

0.250

0.300

A r c l e n g t h ( m )

l1 l2 l3

-0.0100

-0.0050

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

E l e c t r o d e s s p e e d

v1 v2 v3

Shortcircuitregime

Maximum arclength

Fig. 4. The variation of active and reactive power, drop voltage, arc length and electrodes speed





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3.2 Simulation of the active power control

system’s operation following the reactive

power’s compensation and filtration of the

harmonic currentsTo simulate the operation of the power control

system in different regimes using the reactive power’s filtration and compensation installation, it

was used the diagram presented in fig. 5. This

condition contains the 4 filters on the harmonics

5,7,11 and 13 and the reactive power compensation

installation composed by the constant part (in Y

connection) and the adjustable part in steps. The

values of the elements are the ones designed in [7]

and [8].

RL

RL

A

B

C

RL

A

B

C

A

B

C30 [kV]

#2#1

110 [kV]

100 [MVA] A

B

C

A

B

C0.6 [kV]

#2#1

30kV

73.0 [MVA]0.00000934 [H]

0.00000934H

0.00000934 [H]

Uj2

Um1

Um2

Im1

Im2

The passive filters for 5, 7, 11 and 13harmonics

Furnacetransformer

Uj3

Im3

Um3

Uj1

P ow er

A B

P Q

A

B

C

A

B

C

.1 [ohm]

.1 [ohm]

.1 [ohm]

PRMS

RMS

A

B Compar-ator 0.0

D+

F

+

-0.5

*

2.0

*Q

4 7 . 5

2 [ u F ]

4 7 . 5

2 [ u F ]

4 7 . 5

2 [ u F ]

C +

C +

C +

0 . 0 1 7 5 9 [ H ]

2 3 . 0 4 [ uF ]

0 . 0 1 7 5 9 [ H ]

2 3 . 0 4 [ uF ]

0 . 0 1 7 5 9 [ H ]

2 3 . 0 4 [ uF ]

0 . 0 2 3 9 3 [ H ]

8 . 6 4 [ uF ]

0 . 0 2 3 9 3 [ H ]

8 . 6 4 [ uF ]

0 . 0 2 3 9 3 [ H ]

8 . 6 4 [ uF ]

0 . 0 1 4 5 4 [ H ]

5 .7 6 [ uF ]

0 . 0 1 4 5 4 [ H ]

5 .7 6 uF ]

0 . 0 1 4 5 4 [ H ]

5 .7 6 [ uF ]

0 . 0 1 0 4 1 [ H ]

5 .7 6 uF ]

0 . 0 1 0 4 1 [ H ]

5 .7 6 uF ]

0 . 0 1 0 4 1 H ]

5 .7 6 [ uF ]

P

The threephase electricarc model

6.9 e-3 [ohm]

3.64 e-3 [ohm]

0.372e-3[ohm]

RA 1 +

RA 2 +

RA 3 +

HV-MVtransformer The three

phase variablecapacities

Fig. 5. The PSCAD simulation scheme for EAF with harmonics filters and power compensation installation

To ensure the reactive power’s compensation on the

entire duration of the active power’s control process

it is necessary that, depending on the reactive

power’s momentary value, to connect or disconnectone compensation step at a time.

Choosing of the compensation step is made as

follow:

- If the reactive power is situated within the

range –4,00 ÷ 4,00 MVAR the

compensation step does not modify;

- If the reactive power is higher than 4,00

MVAR a new compensation step will be

introduced;

- If the reactive power is lower than - 4,00

MVAR a compensation step will bedisconnected.

The PSCAD simulation scheme for choosing

compensation step is depicted in fig. 6.

In [10] was presented the powers dependency by the

drop voltage. Thus, in [10] was show that active power reaches up to a maximum value for a certain

value of the drop voltage. Therefore, the active

power dependency by the drop voltage is a

monotone increasing function for drop voltage

values between 0 and a value corresponding to

maximum active power. For these values the

dependency of active power/drop voltage is a

bijective function. Because the drop voltage

depends linearly by the electric arc’s length, it

results that also the active power depends on the

electric arc’s length. Based on these remarks, the

active power’s iterative adjustment algorithm

proposed by the de authors is based on the





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modification of the electric arc’s length depending

on the active power desired to be obtained.

Assuming that at iteration n the arc’s length is ( )nl ,and the active power is ( )nP , the arc’s length atiteration will be given by the relation1+n

( ) ( ) (nenlnl ⋅+=+ )α 1 (4)where

(5)( ) ( )nPPne −= 0are the error by which is obtained the imposed

active power P0 at iteration n, and α represents an

adapting factor. It is obvious that if the value of the

active power obtained at iteration n is higher than

the value of the imposed active power P0 is

necessary to reduce the electric arc’s length and

opposite, fact ensured by the presented algorithm.

[9], [11]. This algorithm is known as the LMS

algorithm (Least Mean Square) or the stochastic

gradient’s algorithm, being, due to its simplicity, the

most used algorithm implemented in the current

systems. Choosing of the adapting factor’s values is

made taking into account its influence upon the

algorithm’s main characteristics: the algorithm’s

convergence speed and the adjustment error.

Were obtained the results presented in fig. 7 for an

adapting factor’s value 000001,0=α and in figure 8

for an adapting factor’s value α=0,000005.

.

Determination of direction for reactive power compensation

The calculus of equivalent capacity

D+

F

+14.4

Cstep

Q

f

f

*Cech

C

Clear

1sT

A

B Compar-ator

Mono-

T

stable A

B Compar-ator

Mono-

T

stable-4.17

4.17

*

-1.0

D+

F

+

CN

D

N/D

3.0

Fig. 6. The PSCAD simulation scheme for choosing compensation step. The calculus for equivalent capacity

4 Conclusion

By using harmonics filters, load balancing and

reactive power compensation the functioning regime

of the UHP EAF can be improve by controlling the

active power. For higher values of the adapting

factor allow the obtaining of higher convergence

speed of the control algorithm, but the dispersion

obtained around the desired value is higher, the

algorithm being possible to lose the convergence.

Smaller values of the adapting factor allow the

obtaining of a smaller dispersion of the system

output’s values but the convergence speed is

smaller.





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0.0 5.0 10.0 15.0 20.0

0

10

20

30

40

50


P P0

0

1020

30

40

50

60

70

80

90

100

R e a c t i v e p o w e r ( M V A R )

Q

0

20

40

60

80

100

120

E q u i v a l e n t c a p a c i t y ( m i c r o F )

C

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

T h e a r c l e n g t h ( m )

l1 l2 l3

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.200

T h e a r c d r o p v o l t a g e ( k V )

Ust1 Ust2 Ust3

Fig. 7 Variation of active power (impose and simulated), reactive power, equivalent capacity, arc lengths and

drop voltages for α=0.000001





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0.0 5.0 10.0 15.0 20.0

0

10

20

30

40

50


P P0

-20

-10

010

20

3040

50

60

70

80

90

R e a c t i v e

p o w e r ( M V A R )

Q

0

25

50

75

100

125

150

175

200

225

E q u i v a l e n t c a p a c i t y ( m i c r o F )

C

0.000

0.025

0.050

0.075

0.100

0.125

0.150

0.175

0.200

0.225

T h e a r c l e n g t h ( m )

l1 l2 l3

0.025

0.050

0.075

0.100

0.125

0.150

0.175

0.200

0.225

0.250

T h e a r c d r o p v o l t a g e ( k V )

Ust1 Ust2 Ust3

Fig. 7 Variation of active power (impose and simulated), reactive power, equivalent capacity, arc lengths and

drop voltages for α=0.000005





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References:

[1] “IEEE recommended practice for monitoring

electric power quality”. Standard IEEE std.

1159-1995

[2] Montanari, G.C., Loggini, M., Cavallini, A.,

Pitti, L., Zaminelli, D. (1994), Arc-Furnace

model for the Study of Flicker Compensation

in Electrical Networks, IEEE Transactions on

Power Delivery, vol. 9, No. 4, pg. 2026-2036.

[3] Tang, L., Kolluri, S., Mark, F. Mc-Granaghan,

Voltage Flicker Prediction for two

simultaneously operated Arc Furnaces, IEEE

Trans. on Power Delivery, vol. 12, No. 2, 1997.

[4] Panoiu M, Panoiu C, Modeling and simulating

the AC electric arc using PSCAD EMTDC,

Proceedings of the 5th WSEAS Int. Conf. onSystem Science and Simulation in Engineering,

Tenerife, Spain, Dec. 16-18, 2006

[5] Panoiu M., Panoiu C., Osaci M, Muscalagiu I.,

Simulation Result about harmonics filtering for

Improving the Functioning Regime of the UHP

EAF, Proceedings of the 7th WSEAS Int. Conf. on

Signal Processing, Computational Geometry and

Artificial Vision ,Vouliagmeni Beach, Athens,

Greece, Aug. 24-26, 2007, pg. 71-76


Simulation Results for Modeling the AC Electric

Arc as Nonlinear Element using PSCAD

EMTDC, WSEAS Transaction on circuits and

systems, pp 149-156. vol 6, 2007


Simulation Result about Harmonics Filtering

using Measurement of Some Electrical Items in

Electrical Installation on UHP EAF, WSEAS

Transaction on circuits and systems, vol 7, Jan

2008, pp 22-31.

[8] Panoiu M., Panoiu C., Sora I, Iordan A., Rob R.,

Using Simulation for study the Possibility of

Canceling Load Unbalance of non-sinusoidal

High Power three-phase Loads, WSEAS

TRANSACTIONS on SYSTEMS , Issue 7, Volume

7, July 2008, pp 699-710, ISSN: 1109-2777

[9] Alexander, S. T., Adaptive Signal Processing,

Springer Verlag New York Inc., 1986.[10] Panoiu M, Panoiu C, Sora I, Osaci M, About the

possibility of power controlling in the Three-

Phase Electric Arc Furnaces using PSCAD

EMTDC simulation program, Advances in

Electrical and Computer Engineering , vol. 7,

number 1 (27), 2007, ISSN 1582-7445, pp 38-43

[11] Yuu-Seng Lau; Hussian, Z.M.; Harris, R., A

time-dependent LMS algorithm for adaptive

filtering, WSEAS Transactions on Circuits and

Systems, v 3, n 1, Jan. 2004, p 35-42

[12] www.pscad.com



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CONTROL DEL ARCO ELECTRICO.pdf